<!DOCTYPE html>
<html lang="en">
    <head>
        <meta charset="UTF-8">
        <meta name="viewport" content="width=device-width, initial-scale=1.0">
        <title>display</title>
        <style>
            *{
                margin: 0;
                padding: 0;
            }
            div {
                width: 1000px;
                height: 50px;
                background: pink;
                margin: auto;
            }
            ul li{
                width: 250px;
                height: 50px;
                list-style: none;
                line-height: 50px;
                text-align: center;
                float: left;
            }
            li p:nth-child(2){
                display: none;
            }
            li:hover p:nth-child(1){
                 display: none;
             }
            li:hover p:nth-child(2){
                display: block;
            }
        </style>
    </head>
    <body>
        <div>
            <ul>
                <li>
                    <p>s1</p>
                    <p>s1.1</p>
                </li>
                <li>
                    <p>s2</p>
                    <p>s2.1</p>
                </li>
                <li>
                    <p>s3</p>
                    <p>s3.1</p>
                </li>
                <li>
                    <p>s4</p>
                    <p>s4.1</p>
                </li>
            </ul>
        </div>
    </body>
</html>